Gear box for hydraulic energy recovery

ABSTRACT

A hydraulic energy recovery and a mechanical drive system in one unit that also provides integral mounting of hydraulic pump/motors for primary drive, secondary drive, and pumps for cooling, lubrication, and low pressure systems along with a mounting position for a power take-off device.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/674,031 filed Apr. 22, 2005, U.S. Provisional Application No.60/764,908 filed Feb. 3, 2006, and U.S. Provisional Application No.60/775,105 filed Feb. 21, 2006, all of which are hereby incorporated byreference in their entireties.

FIELD OF THE INVENTION

This invention relates generally to a unitized vehicle drive system thatprovides both hydraulic energy storage and recovery along with a directmechanical drive mode for maximum fuel consumption efficiency throughoutthe vehicle's duty cycle. The drive system can be used on a variety ofvehicle types, including in particular garbage collection vehicles andother vehicles that make frequent starts and stops, and which at leastpart of the time need to travel at “on-highway” speeds.

BACKGROUND OF THE INVENTION

For many years there has been recognition that vehicles could be mademore fuel-efficient if the energy normally lost in decelerating orbraking the vehicle could be somehow collected, stored and reused toaccelerate the vehicle. A relatively large number of prior patents andpublished patent applications exist which are directed to variousaspects of this general approach. Some have proposed to collect andstore the energy in hydraulic accumulators and then reuse the energythrough fixed or variable displacement hydraulic transmissions. Avariation of this concept utilized a flywheel as an energy storagedevice for collecting and storing vehicle deceleration energy, eitheralone or in combination with a hydraulic accumulator.

Many of the previously disclosed systems do not lend themselves to usein existing truck designs whereas others require specially fabricatedhydrostatic drive components.

Some systems heretofore have used a transmission including a hydrostatictransmission portion and a mechanical transmission portion. A typicalhydrostatic transmission comprises a variable-displacement pumphydraulically coupled to a motor (typically, of fixed displacement), andappropriate controls for varying the displacement of the pump. The“mechanical transmission” may comprise a two-speed, shiftable, gear-typetransmission that allows the hydrostatic transmission to use smaller andless expensive components. A problem with some hydrostatic transmissionshas been the need to stop the vehicle to shift between different gearratios.

One solution to this problem is described in U.S. Pat. No. 6,202,016which discloses a hydrostatic transmission that can be shifted “on thego”. The transmission includes a mechanical transmission that isprovided with a shift cylinder having a neutral position, a low gearposition and a high gear position. The hydrostatic transmission iselectronically controlled so that displacement of a variabledisplacement pump is coordinated with the shifting of the mechanicaltransmission to achieve the shift-on-the-go capability. The transmissiondisclosed in this patent, however, limits the ability to optimallycontrol engine speed and pump displacement independently of existingdriving conditions, nor does such transmission lend itself to efficientoperation at “on highway” speeds, typically speeds greater than 40 mph.

SUMMARY OF THE INVENTION

The present invention not only provides both a hydraulic energy recoveryand a mechanical drive system in one unit but also provides integralmounting of hydraulic pump/motors for primary drive, secondary drive,and pumps for cooling, lubrication, and low pressure systems along witha mounting position for a power take-off (PTO) device. A preferredembodiment is for use with an internal combustion (IC) engine, but couldbe powered by other forms of prime movers such as gas turbines, electricmotors and fuel cells.

According to one aspect of the invention, a power transfer apparatus fora vehicle comprises a housing having an axis, a power input shaft at oneaxial end of the housing that is connectable to a prime mover of thevehicle for receiving power from the prime mover, an output drive shaftat an opposite axial end of the housing that is connectable to one ormore wheels of the vehicle for transfer of power to the one or morewheels, a primary hydraulic pump mounted to a first axial end of thehousing, a hydraulic motor mounted to an opposite second axial end ofthe housing, and a transmission assembly contained within the housing,which the transmission assembly includes a pump coupling for couplingthe primary hydraulic pump to the power input shaft, and a motorcoupling for coupling the hydraulic motor to the output drive shaft.

In a preferred embodiment, the primary hydraulic pump and motor haverespective rotational drive shafts extending parallel to the power inputand output drive shafts, and a plurality of hydraulic motors are mountedto the second axial end of the housing. Primary hydraulic pump powercircuitry transfers hydraulic power from the primary hydraulic pump toan energy storage device, as does hydraulic motor power circuitry duringuse of the hydraulic motor as a pump to effect braking of the vehicleand energy regeneration.

According to another aspect of the invention, a power transfer apparatusfor a vehicle comprises a power input shaft that is connectable to aprime mover of the vehicle for receiving power from the prime mover, anoutput drive shaft that is connectable to one or more wheels of thevehicle for transfer of power to the one or more wheels, a primaryhydraulic pump, a variable displacement hydraulic motor, a transmissionassembly including a pump coupling for coupling the primary hydraulicpump to the power input shaft and a motor coupling for coupling thehydraulic motor to the output drive shaft, and hydraulic power circuitryfor directly or indirectly supplying hydraulic power from the hydraulicpump to the hydraulic motor. The transmission assembly includes amechanical transmission connected between the hydraulic motor and theoutput drive shaft, and the mechanical transmission has first and secondgear ratios and a clutch for shifting between the first and second gearratios. The displacement of the hydraulic motor is controlled by acontroller to synchronize the speed and/or torque output of thehydraulic motor to the rotational speed of the output drive shaft forshifting between the first and second gear ratios while the output driveshaft is rotating. Consequently, this enables the displacement of theprimary hydraulic pump and/or speed of the prime mover to be optimizedfor any given driving condition.

In other words, the present invention enables shifting “on the go” to becontrolled by a variable displacement drive motor or motors adjusted toramp rotational speed through an acceptable speed range, and then toinitiate the shift actuation signal at the proper time to meetsynchronization during the ramp up or ramp down in speed. The pressuresource can be supplied by an accumulator system with a variable volumepump at a fixed or zero stroke during the synchronization phase.Shifting can be effected even when only a fixed volume pump is used tosupply pressurized fluid to maintain a charge in the accumulator system.The shifting process may also be applied not only for increasing anddecreasing gear ranges but also changing between mechanical andhydraulic drives.

The pump and accumulator try to maintain a pressure defined by theoperating conditions of the vehicle or machine being driven. Thehydraulic motors are hydraulic machines that either convert hydraulicpressure into rotational mechanical energy or convert rotationalmechanical energy into hydraulic pressure. The process works whether thechange in ratio is increasing or decreasing, or the machine changes fromhydraulic drive to or from mechanical drive.

According to a further aspect of the invention, provision is made forcontinued hydraulic braking even when the energy storage device cannotaccept any more energy. This is accomplished by directing flow from oneor more hydraulic motors that are being reversely driven as pumps tothrough a pressure relief valve so that the hydraulic system willcontinue to absorb energy and thereby continue to effect vehicle brakingof the vehicle when braking is still be commanded.

According to still another aspect of the invention, an apparatus forminga portion of a vehicle drive system, comprises a hydraulic motor; and agear assembly, the gear assembly, in a first mode, enabling the motor todrive wheels of the vehicle and, in a second mode, providing a directmechanical connection to the wheels of the vehicle with an engine of thevehicle for enabling the engine to drive the wheels.

As will be appreciated by those skilled in the art, one or more of theprinciples of the present invention can be applied to any hydraulicdrive system employing one or more variable displacement drive motorswith or without the feature of hydraulic energy recovery.

Further features of the invention will become apparent from thefollowing detailed description when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary vehicle drivesystem including a power drive unit according to the Invention.

FIG. 2 is a diagrammatic illustration of the power drive unit of FIG. 1,showing the unit in a neutral state.

FIG. 3 is a diagrammatic illustration of the power drive unit of FIG. 1,showing the unit in a direct drive mode.

FIG. 4 is a diagrammatic illustration of the power drive unit of FIG. 1,showing the unit in a braking/accumulator charging state.

FIG. 5 is a diagrammatic illustration of the power drive unit of FIG. 1,showing the unit in a hydrostatic drive mode in low gear.

FIG. 6 is a diagrammatic illustration of the power drive unit of FIG. 1,showing the unit in the hydrostatic drive mode in high gear.

FIG. 7 is a chart showing a clutch and gear train sequence for the powerdrive unit.

FIG. 8 is a rear end view of an exemplary power drive unit.

FIG. 9 is a front end view of the power drive unit of FIG. 8.

FIG. 10 is a side elevational view of the power drive unit.

FIG. 11 is a top view of the power drive unit, shown installed in theframe of a vehicle.

FIG. 12 is a perspective view of the power drive unit with the hydraulicpumps and motors removed to show the transmission assembly.

FIG. 13 is an end elevational view of the transmission assembly.

FIG. 14 is a cross-sectional view through the transmission assembly,taken along the line A-A of FIG. 13.

FIG. 15 is a cross-sectional view through the transmission assembly,taken along the line B-B of FIG. 13.

FIG. 16 is a cross-sectional view through the transmission assembly,taken along the line C-C of FIG. 13.

FIG. 17 is a fragmentary cross-sectional view of the transmissionassembly, taken along the line D-D of FIG. 13.

FIG. 18 is a fragmentary side elevational view of the transmissionassembly, looking from the arrow X of FIG. 13.

DETAILED DESCRIPTION

Referring now in detail to the drawings and initially to FIG. 1, anexemplary vehicle drive system according to the present invention isindicated generally by reference numeral 20. The vehicle drive system 20includes a power drive unit 21 connected between a prime mover 22 andthe drive wheel or wheels 23 of a vehicle generally denoted by referencenumeral 24. The prime mover preferably is an internal combustion (IC)engine, but other prime movers could also be used, such as gas turbines,electric motors and fuel cells. The power drive unit includes a powerinput shaft 26 to which the engine is drivingly connected by anysuitable means and an output drive shaft 27 drivingly connected to oneor more the wheels 23 of the vehicle by any suitable means, such as by adrive shaft 29 and transaxle 30.

The power drive unit 21 is characterized by a housing 33 that provides amount for one or more primary hydraulic pumps 34 and one or morehydraulic drive motors 35 (two being shown). The embodiment shown inFIG. 1 utilizes one reversible pump/motor unit 34 and two reversiblemotor/pump units 35 to drive the vehicle in a city or working mode. Thisarrangement optimizes the packaging of these units into the unitizedtransmission by using lower cost standard hydraulic units. It alsopermits more economical gearing from the dual power paths (lower toothloading), more responsive shift times (less mechanical inertia), asmaller overall package size and weight, and generally smootheroperation.

Each pump 34 and motor 35 preferably is of a variable displacement type,and each preferably can be reversely driven to function as a motor orpump, respectively. By way of example, the pumps and motors may be axialpiston pumps and motors, wherein displacement of the pump/motor isvaried by changing the tilt angle of a tiltable swash plate, in a mannerthat is well known to those skilled in the art.

The housing contains a transmission assembly 37 to which the power inputshaft 26 and output drive shaft 27 are connected. The housing furtherprovides a mount for one or more auxiliary pumps 39 for cooling,lubrication, and/or low pressure systems along with a mounting positionfor a power take-off (PTO) device 40 that may be used to providehydraulic power to other parts of the vehicle via a hydraulic systemseparate from the hydraulic system of the power drive unit (except thatpower for the PTO device is taken off the power drive unit. Theauxiliary pumps may be a stacked arrangement of pumps, particularlypositive displacement pumps, driven by a common drive shaft. As depictedin FIG. 1, one auxiliary pump may circulate hydraulic fluid through acooler 42 and back to a reservoir 43. Another auxiliary pump may be usedto supply pressurized fluid to the transmission assembly 37 and/or otherdrive components for lubrication, and another auxiliary pump may be usedto supply low pressure fluid to components of the hereinafter describedhydraulic circuits to operate, for example, pilot valves used to controlfluid pressure components.

As illustrated in FIG. 1, the primary pump 34 is mounted to one axialend of the housing while the hydraulic motors 35 are mounted to theopposite axial end of the housing. In addition, the auxiliary pumps 39are mounted to the same axial side of the housing as the primary pump34. It is noted that in accordance with one or more aspects of theinvention, the motors and/or pumps may be otherwise mounted. Forexample, the primary pump could be separately mounted, such as to theengine.

The vehicle drive system 20 further comprises an energy storage device46. In the illustrated embodiment the energy storage device is anaccumulator system including one or more pressurized fluid accumulators47, specifically hydropneumatic accumulators. Other energy storagedevices may be used such as a mechanical fly wheel or batteries. Theaccumulators 47 are supplied with pressurized fluid from the primarypump 34 and/or motors 35 by means of a high pressure manifold and fluidcircuitry generally indicated at 50. The fluid circuitry 50 is commandedby a system controller 52, more particularly an electronic systemcontroller, to control the flow of pressurized fluid to and from theaccumulators 47, the pump 34, motors 35 and other hydraulic components,including a flow restrictor 55, the function of which is discussedbelow. The system controller may include one or more microprocessors andassociated components programmed to carry out the herein describedoperations. The controller may have various inputs for receiving datafrom various sensors that monitor various operational parameters of thevehicle and various outputs by which the controller commands variousoperations.

Referring now to FIG. 2, the transmission assembly 37 can be seen toinclude a primary pump clutch C1 for selectively drivingly coupling theprimary pump to the power input shaft 26, a direct drive shaftengagement clutch C2 for selectively drivingly coupling the output driveshaft 27 to the power input shaft 26, and a gear selector switch C3 forswitching a mechanical transmission 58 between neutral, hydro low andhydro high states.

The clutch C1 may be of any suitable type, although a wet multi-plateslip clutch is preferred to allow the clutch to be engaged withouthaving to synchronize the speed of the primary pump to the speed of thepower input shaft. As shown, the clutch can be engaged to couple a gear60 that is rotatably coupled to the drive shaft 61 of the primary pump34 to a gear 62 that is rotatably coupled to the power input shaft 26.Engagement and disengagement of the clutch C1 may be effected by a fluidpressure actuator (not shown) controlled by the electronic systemcontroller 52 (FIG. 1).

The clutch C2 may be of any suitable type, such as a jaw or square toothclutch that provides for transfer of high torques without slippage. Onejaw of the clutch may be fixedly rotatably coupled to the power inputshaft 26 (or more particularly to the gear 62) and the other movable jawmay be keyed to the output drive shaft 27 and shifted axially by adirect drive shift cylinder (not shown in FIG. 2) to engage anddisengage the jaws. The direct drive shift cylinder may be controlled ina conventional manner by the electronic system controller 52 (FIG. 1).

The clutch C3 may be of any suitable type, such as a three position jawor square tooth clutch that provides for transfer of high torqueswithout slippage. The clutch includes jaws respectively fixed to gears65 and 66 and a movable jaw keyed to the output drive shaft 27 andshifted axially by a gear shift cylinder (not shown in FIG. 2) between aneutral position disengaged from the gears 65 and 66 as depicted in FIG.2, a hydro low (low gear) position depicted in FIG. 5, and a hydro high(high gear) position depicted in FIG. 6. The gears 65 and 66 are meshedwith respective gears 71 and 72 on a gear shaft that is rotatablycoupled to the drive shaft 74 of each hydraulic motor 35. The gear toothratios may be selected to provide desired hydro low and hydro high speedratios between the motor drive shafts and the output drive shaft. Thegear shift cylinder may be controlled in a conventional manner by theelectronic system controller 52 (FIG. 1).

As seen in FIG. 2, the power input shaft 26 may be provided with a yoke76 for connection to the prime mover 22 (FIG. 1). Similarly, the outputdrive shaft 27 may be provided with a yoke 77 for connection to thevehicle drive shaft 29 (FIG. 1).

It can also be seen in FIG. 2 that the several drive shafts of thepumps, motors and transmission assembly are all parallel with oneanother and with the power input and output drive shafts. In addition,the drive output shaft 27 may be coaxial with the power input shaft 26.Likewise, the drive shaft 61 of the primary pump 34 may be coaxial withthe drive shaft 74 of one of the hydraulic motors 35 and the drive shaft80 of the auxiliary pumps 39 may be coaxial with the drive shaft of theother hydraulic motor. The illustrated arrangement of the pumps, motorsand drive shafts in association with the housing 33 provide a compact,unitized power drive unit. The drive shaft 80 has rotatably coupledthereto a gear 82 in mesh with the gear 62 whereby the auxiliary pumpsare driven by the power input shaft.

In normal operation, the vehicle will be at a stopped condition with thetransmission in neutral as shown in FIG. 2, where the clutches C1, C2and C3 are all disengaged. With the clutches C2 and C3 disengaged, thetransmission assembly will be in neutral, with no power being suppliedto the drive wheels nor any braking function being effected by the drivemotors.

The controller 52 may engage the clutch C1 while the engine is runningto drive the primary pump 34. The high pressure manifold and fluidcircuitry 50 includes valves (which may be integral in the housing) fordirecting pressurized hydraulic fluid from the primary pump to theaccumulator system 46 to build up a controlled volume of hydraulic fluidunder pressure. The accumulator system 46, as above indicated, mayconsist of a single accumulator or a bank of two or more units dependingon the total volume of hydraulic fluid needed to store in the system fora given application. The flow from the primary pump is also available tosupply the drive motors 35 for use in driving the vehicle. The primarypump may be commanded to supply pressurized fluid to the high pressuremanifold and fluid circuitry as a function of the flow of pressurizedfluid to or from the drive motors 35 and the energy stored in theaccumulator system 46.

If the pressure level or other sensor input indicates that theaccumulator system 46 is fully charged, then the electronic systemcontroller 52 can disengage dutch C1 to the primary pump 34 and/or shutoff the engine 22, conserving fuel until additional power is needed.

The clutches C2 and C3 may be operated by the controller 52 to providetwo modes of vehicle operation, a first mode, also herein referred to asthe city mode or work cycle mode, and a second mode, also hereinreferred to as the highway mode. In the first mode, the clutch C2 isdisengaged and the clutch C3 is operated by the controller 52 to shiftbetween neutral and one or more gear speeds between the drive motors 35and the output drive shaft 27. In the city mode or work cycle mode, thepower drive unit 21 is configured to efficiently and effectivelyaccommodate frequent stop and go operation at low speeds, for exampleless than 40 mph, as the drive motors 35 drive the vehicle through themultiple speed mechanical transmission 58 (although it should bementioned that a single speed transmission could also be employed or atransmission having three, four or more speeds, i.e. gear ratios).

In the first mode of operation, the position of the vehicle'saccelerator and brake pedals may be detected by sensors and act as inputcommands to the electronic system controller 52. If the desired actionis to accelerate, say from a stop position, then the electronic systemcontroller 52 will shift clutch C3 to engage the gear 65 to shift themechanical transmission into its hydro low position illustrated in FIG.5 to start the vehicle in motion. The output drive shaft and the drivemotors initially will not be rotating so the clutch can engage gear 65connecting it to the output drive shaft 27. The controller may thencommand the high pressure manifold and hydraulic circuitry 50 to supplyhigh pressure fluid from the accumulator system 46 and/or the primarypump 34 (if then operating) to the hydraulic drive motors 35 to drivethe output drive shaft 27 through the mechanical transmission 58. Thisin turn will drive the drive wheels 23 of the vehicle to accelerate thevehicle from the stopped position. The displacement of the drive motorsmay be varied by the controller 52 to control the rate of accelerationto increase or maintain a constant speed (zero acceleration). Each drivemotor may have the swash plate thereof set to maximum displacement. Thiswill drive gear 65 through gear 71 to start the vehicle into motion. Byreducing the swash plate angle the drive motors will rotate faster for afixed volume of oil delivered to the drive motors, thereby acceleratingthe vehicle to a higher speed. The drive motors can operate to deliverhigh torque to the drive wheels of the vehicle.

If the vehicle is already moving and a desired action is to decelerateor brake the vehicle, the electronic system controller 52 directs thehigh pressure manifold and fluid circuitry 50 to receive high pressurefluid from the drive motors 35 which then will be reversely driven andact as pumps, thereby delivering high pressure fluid back to theaccumulator system 46. The hydraulic drive motors, acting as pumps, willgenerate resistance in the drive train to slow the vehicle down. Thisaction also recovers most of the kinetic energy from the vehicle andstores it in the accumulator system for future use by the drive systemor for performing other hydraulically powered work related tasks on thevehicle.

The vehicle may be provided with mechanical brakes that normally willnot be needed to decelerate the vehicle, but which will be available foruse if the braking force required (such as a panic stop) is greater thanthat which is being generated by the reversely driven hydraulic motorsacting as pumps, or as a back-up in case of a failure in the hydraulicdrive system.

The stored energy in the accumulator system 46 can be used forpropelling the vehicle in the city or working mode with the engine offuntil the accumulator system signals the electronic system controller 52that it is getting low on fluid and needs to be refilled. At this point,the electronic system controller 52 may operate the primary pump as amotor. That is, the electronic system controller may direct the highpressure manifold and fluid circuitry 50 to supply high pressure fluidfrom the accumulator system 46 to the primary pump (then acting as amotor) with the clutch C1 engaged, to turn the engine 22 and therebyrestart the engine. Once the engine is started, the primary pump 34 isagain reversed to act as a pump and deliver high pressure fluid backthrough the high pressure manifold and fluid circuitry to theaccumulator system for replenishment. This sequence can repeatcontinuously during city or working mode resulting in significantsavings in fuel consumption. Moreover, the engine speed and displacementof the primary pump may be optimized to maintain the accumulator systemat a desired level while pressurized fluid is intermittently withdrawnfrom the accumulator system as needed to drive the hydraulic motors fordriving the drive wheel or wheels of the vehicle. That is, the enginecan be operated in a desired range that minimizes pollutants whilemaximizing fuel economy. Generally it is desirable to run the engine asslow as possible, or not at all, even while the power requirements ofthe vehicle can vary significantly.

In the illustrated embodiment, the city or work mode uses the two speedmechanical transmission 58 to cover respective speed ranges so that thehydraulic drive motors 35 can be operated within their most efficientspeed ranges. For example, the hydro low gear ratio can be used to covervehicle speeds from 0 to about 25 mph and the hydro high gear ratio canbe used to cover vehicle speeds from about 25 to about 40 mph. Theselection of the shifting point is set by the electronic systemcontroller 52 software or can be manually selected by the vehicleoperator depending upon desired duty cycle and operating conditions. Theshift points do not have to be speed related but can be modified orcontrolled by other sensor inputs such as vehicle incline angle, grossloaded weight, ambient temperature, hydraulic fluid temperature, orother performance influencing factors.

Once the vehicle has accelerated to or past the upper end of the hydrolow range, such as about 25 mph, the electronic system controller 52commands the transmission assembly 37 to shift to the hydro high gearratio. Since both gear sets of the hydraulic drive motors are inconstant mesh and shifting is accomplished by the clutch C3 capable ofselecting “neutral” for idle and direct drive, hydro low or hydro high,it is possible to control the speed of the drive motors forsynchronization to achieve a smooth shift either up or down. This can beaccomplished by using the stored hydraulic fluid from the accumulatorsystem 46 independent of the speed or displacement of the primary pump34. More particularly, the displacement of the hydraulic drive motors 35may be controlled by the electronic system controller 52 to synchronizethe speed and/or torque output of the hydraulic drive motors to therotational speed of the output drive shaft 27 for shifting between thefirst and second gear ratios while the output drive shaft is rotating.Consequently, shifting is effected without having to vary thedisplacement of the primary pump 34, as is desired.

More particularly, shifting from the hydro low gear ratio to the hydrohigh gear ratio can be initiated by varying the displacement of thedrive motors (by varying the tilt angle of a swash plate) such that noor a minimal amount of torque is being transferred between the drivemotors and the drive shaft 27. This allows the clutch C3 to be easilyshifted into neutral. Alternatively, the controller could command thehigh pressure manifold and fluid circuitry to reduce pressure or flowfrom the accumulator system to the drive motors and achieve the samereduction in torque to allow the shift of clutch C3 into neutral.

After the clutch C3 is shifted into neutral, the displacement of thedrive motors and/or the flow of fluid from the accumulator system can bechanged to synchronize the speed of the gear 66 to be newly engaged bythe clutch C3 to the speed of the output drive shaft 27. Due to thegearing ratio between gear sets 65/71 and 66/72, gear 66 will initiallybe rotating at a higher speed than the output drive shaft and a smoothengagement between gear 66 and the output drive shaft normally cannot bemade. As the rotating speed of the drive motors continues to ramp down,the rotating speed of gear 66 will pass through that of the output driveshaft. The controller will command the clutch C3 actuator to movetowards the hydro high position and synchronously engage gear 66 withthe output drive shaft as depicted in FIG. 5, whereupon the mechanicaltransmission will be in hydro high. When in hydro high, the displacementof the drive motors and/or the flow of fluid from the high pressuremanifold to the drive motors may be controlled to control theacceleration (or deceleration) of the vehicle within the hydro highrange, such as from 25 to 40 mph.

For those skilled in the art, the shifting from hydro high back to hydrolow can be accomplished by basically reversing the previous sequence.

If the vehicle operator commands the vehicle to be accelerated to orpast the top speed of the city or working mode setting, such as about 40mph, the electronic system controller 52 commands the transmissionassembly 37 to shift into the second or highway mode. To this end, theclutch C2 is engaged as depicted in FIG. 3, whereupon the engine 22 willdirectly drive (rather than hydrostatically drive) the driven wheel orwheels of the vehicle. In a manner similar to that described above,shifting from the hydrostatic drive to direct drive can be initiated byvarying the displacement of the drive motors (by varying the tilt angleof a swash plate) such that no or a minimal amount of torque is beingtransferred between the drive motors and the drive shaft 27. This allowsthe clutch C3 to be easily shifted into neutral. Alternatively, thecontroller could command the high pressure manifold and fluid circuitryto reduce pressure or flow from the accumulator system to the drivemotors and achieve the same reduction in torque to allow the shift ofclutch C3 into neutral. In addition, the speed of the engine can becontrolled by the controller to substantially match the speed of thepower input shaft to the output drive shaft to enable easy engagement ofclutch C2.

In this mode, the engine will be running within it's most efficientspeed range and best fuel economy for highway speeds. The drive motorspreferably will be disengaged from the drive train by clutch C3 set inneutral to further maximize overall vehicle efficiency. However, whenbraking is called for, the clutch C3 may be engaged (with or withoutdisengagement of the clutch C2) whereupon the hydraulic motors, actingas pumps, generate resistance in the drive train to slow the vehicledown and recover kinetic energy from the vehicle for storage in theaccumulators. If the vehicle is being slowed to a stop, the clutch C2may need to be disengaged unless it is desired to shut off the engine.In FIG. 4, a braking/energy regeneration state of the transmissionassembly 37 is depicted, the clutch C3 being engaged and the clutch C2being open. Shifting from direct drive back into to hydro high can beeffected by reversing the sequence described above to achieve a smoothsynchronous shift.

The above described exemplary sequencing of the clutches andcorresponding states of the power drive unit 21 is set forth in thechart shown in FIG. 7.

An advantage afforded by the herein described energy recovery system isin the conservation of the vehicle's mechanical brakes. During normaloperation, kinetic energy from the deceleration or braking mode is fedback into the accumulator system through the high pressure manifold bythe reversely driven drive motors acting as pumps. When the accumulatorsystem is completely full, then excess fluid at high pressure may bedirected through a pressure relief valve so that the hydraulic systemwill continue to absorb kinetic energy, as opposed to simply dumpingflow to the reservoir. This reduces the vehicle's use of mechanicalbrakes and minimizes wear on the brake pads. It also decreases the needto use engine braking, often referred to as “jake braking” and theirattendant noise polluting loud discharge of air.

The unitized construction of the transmission assembly also allows manyif not most of the fluid circuits to be provided internally in thehousing and this minimizes the number and lengths of exposed hydraulicpiping and hose connections. This results in a lower weight and moreeasily mounted units for installation in a variety of vehicles.

An exemplary implementation of the above-described features of theinvention is shown in FIGS. 8-18, wherein the same numbers are used todenote the above described corresponding components. Briefly, FIGS. 8-11show the assembled power drive unit 21 including the housing 33 to whichthe primary pump 34, auxiliary pump 39, and drive pumps 35 are mounted.The power take-off device 40 also can be seen to be mounted to thehousing 33. The housing 33 may be provided with upper mounts 102 and aback support assembly 103 for mounting the power drive unit to the frame105 of the vehicle 24. In FIG. 11, the power drive unit 21 is showninstalled to parallel rails 107 of the vehicle frame 105 inapproximately the same position that would have been occupied by aconventional vehicle transmission. The flywheel housing 109 of theengine is also shown.

In FIGS. 12 and 13 the power drive unit 21 is shown with the pumps andmotors removed. This reveals the mounting surfaces 111 and 112 for theprimary and auxiliary pumps 34 and 39, and the housing will have similarmounting surfaces for the drive motors 35 on the opposite axial end ofthe housing. Also shown are the shift cylinders 114 and 115 for shiftingthe clutches C2 and C3 via respective mechanical linkages 116 and 117,such shift cylinders being conveniently mounted to a side of the housing33. The high pressure manifold assembly also can be seen mounted to thehousing at 118. In addition, the gear assembly for the power take-off 40is seen at 119, such assembly being mechanically connected to the inputdrive shaft and particularly the gear 62 by suitable gearing through anopening 121 in the wall of the housing.

In FIGS. 14-17, details of the clutches C1, C2 and C3 can be seen. Themanner in which the power input shaft and output drive shaft also can beseen. In FIG. 18, the power take-off gear box is further illustrated.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described elements (components, assemblies,devices, compositions, etc.), the terms (including a reference to a“means”) used to describe such elements are intended to correspond,unless otherwise indicated, to any element which performs the specifiedfunction of the described element (i.e., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure which performs the function in the herein illustratedexemplary embodiment or embodiments of the invention. In addition, whilea particular feature of the invention may have been described above withrespect to only one or more of several illustrated embodiments, suchfeature may be combined with one or more other features of the otherembodiments, as may be desired and advantageous for any given orparticular application.

1. A power transfer apparatus for a vehicle comprising a housing having an axis; a power input shaft at one axial end of the housing that is connectable to a prime mover of the vehicle for receiving power from the prime mover; an output drive shaft at an opposite axial end of the housing that is connectable to one or more wheels of the vehicle for transfer of power to the one or more wheels; a primary hydraulic pump mounted to an axial end of the housing; a hydraulic motor mounted to an axial end of the housing; a transmission assembly contained within the housing, the transmission assembly including a pump coupling for coupling the primary hydraulic pump to the power input shaft, and a motor coupling for coupling the hydraulic motor to the output drive shaft; and a secondary hydraulic pump mounted to an axial end of the housing, and the transmission assembly includes a secondary pump coupling for coupling the secondary hydraulic pump to the power input shaft.
 2. An apparatus as set forth in claim 1, wherein the primary hydraulic pump and motor have respective rotational drive shafts extending parallel to the power input and output drive shafts.
 3. An apparatus as set forth in claim 1, wherein the housing includes flow passages connected to a fluid output of the secondary hydraulic pump.
 4. An apparatus as set forth in claim 3, wherein the transmission assembly includes a mechanical transmission connected between the hydraulic motor and the output drive shaft, the mechanical transmission having one or more gear ratios and a clutch for shifting the mechanical transmission, and wherein the clutch is operated by a fluid pressure device to which pressure fluid is supplied from the secondary hydraulic pump.
 5. A vehicle comprising a prime mover, at least one wheel, and an apparatus as set forth in claim 1, wherein the prime mover is drivingly connected to the power input shaft, and the output drive shaft is drivingly connected to at least one wheel of the vehicle.
 6. A vehicle as set forth in claim 5, wherein the prime mover is an internal combustion engine.
 7. A vehicle as set forth in claim 5, wherein the vehicle includes an energy storage device in which energy can be stored, primary hydraulic pump power circuitry for transferring hydraulic power from the primary hydraulic pump to the energy storage device, and hydraulic motor power circuitry for transferring energy from the energy storage device to the hydraulic motor.
 8. A vehicle as set forth in claim 7, wherein the hydraulic motor is reversely operable as a hydraulic pump when driven by the output drive shaft, and the hydraulic motor power circuitry is operable to transfer hydraulic power from the hydraulic motor to the energy storage device when the hydraulic motor is operated as a hydraulic pump.
 9. An apparatus as set forth in claim 1, wherein the primary hydraulic pump and hydraulic motor are mounted to opposite second axial ends of the housing.
 10. An apparatus as set forth in claim 1, wherein the housing encloses an interior space containing the transmission assembly, and the housing has a wall provided with an opening through which a power takeoff device can be coupled to the transmission.
 11. A power transfer apparatus for a vehicle comprising a housing having an axis; a power input shaft at one axial end of the housing that is connectable to a prime mover of the vehicle for receiving power from the prime mover; an output drive shaft at an opposite axial end of the housing that is connectable to one or more wheels of the vehicle for transfer of power to the one or more wheels; a primary hydraulic pump mounted to an axial end of the housing; a hydraulic motor mounted to an axial end of the housing; and a transmission assembly contained within the housing, the transmission assembly including a pump coupling for coupling the primary hydraulic pump to the power input shaft, and a motor coupling for coupling the hydraulic motor to the output drive shaft; and wherein the housing has on an axial side thereof a pump mounting surface against which the primary hydraulic pump is removably sealingly mounted, and the housing has on an axial side thereof a motor mounting surface to which the hydraulic motor is removably sealing mounted.
 12. An apparatus as set forth in claim 11, wherein a plurality of hydraulic motors are each mounted to an axial end of the housing.
 13. An apparatus as set forth in claim 11, further comprising an energy storage device in which energy can be stored, and primary hydraulic pump power circuitry for transferring hydraulic power from the primary hydraulic pump to the energy storage device.
 14. An apparatus as set forth in claim 13, further comprising hydraulic motor power circuitry for transferring energy from the energy storage device to the hydraulic motor.
 15. An apparatus as set forth in claim 14, wherein the hydraulic motor is reversely operable as a hydraulic pump when driven by the output drive shaft, and the hydraulic motor power circuitry is operable to transfer hydraulic power from the hydraulic motor to the energy storage device when the hydraulic motor is operated as a hydraulic pump.
 16. An apparatus as set forth in claim 15, where the energy storage device includes at least one hydropneumatic accumulator, and the primary hydraulic pump power circuitry and hydraulic motor power circuitry includes hydraulic circuits respectively connecting the primary hydraulic pump and hydraulic motor to the at least one hydropneumatic accumulator.
 17. An apparatus as set forth in claim 11, wherein the transmission assembly includes a clutch for selectively drivingly connecting the primary hydraulic pump to the power input shaft.
 18. An apparatus as set forth in claim 11, wherein the transmission assembly includes a clutch for selectively drivingly connecting the output drive shaft to the power input shaft.
 19. An apparatus as set forth in claim 18, wherein the ratio of connection by the clutch is one-to-one.
 20. An apparatus as set forth in claim 11, wherein two said hydraulic motors are mounted at respective mounting surfaces on the same axial side of the housing at opposite sides of a center plane through the housing coplanar with the power input and output drive shafts.
 21. An apparatus as set forth in claim 11, wherein the primary hydraulic pump and hydraulic motor are mounted to opposite second axial ends of the housing.
 22. An apparatus as set forth in claim 11, further comprising an energy storage device in which energy can be stored, and wherein the energy storage device is charged by one or more of the primary hydraulic pump, the hydraulic motor upon reverse driving by the output shaft, and a further pump driven by the output shaft.
 23. An apparatus as set forth in claim 11, wherein the transmission assembly includes a mechanical transmission connected between the hydraulic motor and the output drive shaft, the mechanical transmission has at least one gear ratio and a clutch for shifting into or between multiple gear ratios.
 24. An apparatus as set forth in claim 11, wherein the transmission assembly includes a mechanical transmission connected between the power input shaft and the output drive shaft, the mechanical transmission having a clutch for engaging and disengaging the power input shaft and output drive shaft.
 25. An apparatus as set forth in claim 11, wherein the housing encloses an interior space containing the transmission assembly, and the housing has a wall provided with an opening through which a power takeoff device can be coupled to the transmission.
 26. An apparatus as set forth in claim 11, further comprising an energy storage device in which energy can be stored, and wherein the energy storage device is charged by the hydraulic motor upon reverse driving by the output shaft.
 27. A vehicle comprising: a power transfer apparatus including a housing having an axis, a power input shaft at one axial end of the housing that is connectable to a prime mover of the vehicle for receiving power from the prime mover, an output drive shaft at an opposite axial end of the housing that is connectable to one or more wheels of the vehicle for transfer of power to the one or more wheels, a primary hydraulic pump mounted to an axial end of the housing, a hydraulic motor mounted to an axial end of the housing, a transmission assembly contained within the housing, the transmission assembly including a pump coupling for coupling the primary hydraulic pump to the power input shaft, and a motor coupling for coupling the hydraulic motor to the output drive shaft; an energy storage device in which energy can be stored; primary hydraulic pump power circuitry for transferring hydraulic power from the primary hydraulic pump to the energy storage device; and hydraulic motor power circuitry for transferring energy from the energy storage device to the hydraulic motor; wherein the hydraulic motor is reversely operable as a hydraulic pump when driven by the output drive shaft, and the hydraulic motor power circuitry is operable to transfer hydraulic power from the hydraulic motor to the energy storage device when the hydraulic motor is operated as a hydraulic pump; and wherein the transmission assembly includes a first clutch for selectively drivingly connecting the output drive shaft to the power input shaft, and a second clutch for selectively drivingly connecting the hydraulic motor to the output drive shaft, and further comprising a controller for controlling the first and second clutches for selective connection of the power input shaft to the output shaft for driving the vehicle's wheel or wheels under highway speed conditions, and for connecting the hydraulic motor to the output drive shaft for driving the output shaft in a hydrostatic mode and for energy recovery during braking when the hydraulic motor acts as pump for supplying energy to the energy storage device.
 28. A vehicle as set forth in claim 27, wherein the transmission assembly comprises a third clutch for selectively drivingly connecting the primary hydraulic pump to the power input shaft; and wherein when the first clutch is disengaged the controller is operative to control the third clutch and the speed of the engine for enabling the engine to be operated at an optimal speed for recharging the energy storage device during operation of the vehicle at low speeds, or to be shut off when the energy storage device are sufficiently charged.
 29. A vehicle as set forth in claim 27, wherein the energy storage device includes at least one hydropneumatic accumulator.
 30. A vehicle as set forth in claim 27, wherein the primary hydraulic pump and hydraulic motor are mounted to opposite second axial ends of the housing.
 31. A vehicle as set forth in claim 27, wherein the transmission assembly includes a third clutch for selectively drivingly connecting the primary hydraulic pump to the power input shaft.
 32. A vehicle as set forth in claim 31, wherein the primary hydraulic pump and hydraulic motor are mounted to opposite second axial ends of the housing.
 33. A vehicle as set forth in claim 27, wherein the output drive shaft is driven at low vehicle speeds with high torque in the hydrostatic mode.
 34. An apparatus as set forth in claim 27, wherein the housing encloses an interior space containing the transmission assembly, and the housing has a wall provided with an opening through which a power takeoff device can be coupled to the transmission. 